Short wave tuning device



Nov. 28, 1933. A J, HURT SHORT WAVE TUNING DEVICE Filed Jan. 3', 1951 2sheets-sheet 1 gwvantox NOV. 28, 1933. A, J, HURT 1,936,671

SHORT WAVE TUNING DEVICE Filed Jan. 5,' 1951 2 Sheets-Sheetl 2 f4 a Zi'/2 UNITED STATES PATENT OFFICE SHORT WAVE TUNING DEVICE Arthur J. Hurt,Denver, Colo.

Application January 3, 1931. Serial No. 506,367 3 claims. (c1. 1v1-242)This invention relates to a variable inductance device more particularlydesigned for the reception of short Hertzian waves. Heretofore it hasbeen attempted to tune a short Wave receiving set by means of a varietyof changeable coils of varying inductance. 'Ihis has not beensatisfactory as it is only. an approximate method for only rarely do anyof the -coils provide the exact inductance for the desired wave length.

The principal object of this invention is to provide a tuning coil forshort wave reception,

the turns of which, can be added to or subtracted from so as to minutelyadjust' the inductance to thel desired wave length.

Anothenobject of the invention is to mechanically combine anadjustable-length tuning coil with a variable condenser so that thecorrect inductance-to-capacityratio will be automatically maintained atall settings of the coil.

Still another object of the invention is to provide a tuning coil ofadjustable length, .the turns of which, will 'be shorter as the lowinductance extremity is approached so as to provide means whereby aminute adjustmentof the inductance can be obtained at very short wavelengths and a rapid adjustment at comparatively long wave lengths. Thisconstruction provides a greater number of coils adjacent the gridextremity so thatrit Will oscillate at exceedingly high frequencies andso`that it will eliminate bunching or crowding of the high frequencystations at the grid extremity.

A further object of the invention is to combine a feed back coil with 4avariable length grid or d tuning coil so that 'the feed back effect willbe automatically proportioned according to the.

length of the grid coil.

A further object of the invention is to so construct the variableinductance device that all of the active coils will be maintained inspaced relation from each other so as to maintain a perfect balancethroughout the entire range of adjustment Vwithout 4coil turn contactswhich v would set up objectionable noises in the receiver.

' A still further object is to build a tuning coil in which the turnswill be more widely separated as the grid end is approached so as togive a wider separation at the crowded positions.

Other objects and advantages reside in the detail construction of theinvention, which is designed for simplicity, economy, and efficiency.-These will become more -apparent from the following description.

In the following detailed description of the invention reference is h adto the accompanying drawings which form a part hereof. Like numeralsrefer to like parts in all views of the drawings and throughout thedescription.

able inductance coil combined with a condenser.

Fig. 2 is a front end view thereof.

Fig. 3 is a side elevation thereof, with the condenser eliminated.

Fig. 4 is a vertical, longitudinal section therethrough taken on theline 4 4, Fig. l.

Fig. 5 is a circuit diagram illustrating the 1ncorporation of thevariable inductance coil in a receiving circuit.

Fig. 6 is a. detail view illustrating an alternate form of the insulatedcoil spool.

The invention comprises a front frame l0 and a rear frame 1l joined bymeans of spacer bolts 12. Between the frames 10 and 11 are journalled anupper insulated spool 13 and a lower metallic spool 14. The insulatedspool is preferably slightly conical and is provided with a spiralexternal groove 15 adapted to receive the turns of coils of a bareexible wire 16.

One extremity of the wire 16 is soldered or otherwise secured to oneextremity of the metallicA spool 14 so that it may coil thereabout. Themetallic spool 14 is free to rotate about a lower shaft 1'?, but isconstantly urged in one direction about the shaft 17 by means of a coilspring 18 so as to maintain the wire 16 taut at all times.

One extremity of the coil spring 18 may be secured to one extremity ofthe spool 14. The other` extremity is secured to the shaft 17 by meansof a collar 19 or other suitable fastening device. The insulated spool13 is hollow and cup-shaped,

. the open end of the cup being closed by means of a plug 20 ofinsulating material. The insulated spool 13 is supported on two stubshafts 21 and 22.- The shaft 21 vis affixed in, and projects from,

the plug 20 and rotates in a bearing bushing 23 in the front frame 10.The shaft 22 also projects into the plug 20 but the plug rotatesthereabout so that the shaft 22 remains stationary. An insulated sleeve24 surrounds the shaft 22 and is in 10o turn -surrounded by a relativelyshorter metallic sleeve 25. All of these sleeves and the shaft 22 arerigidly carried in the rear frame 11.

A stationary core block 26 is carried by the shaft 22. The core block 26supports an inner 105 coil cylinder 2'( upon which is wound a feed-backcoil 28. One extremity of the feed-back coil 28 is connected to themetallic sleeve 25 so that the current is carried to the exterior and toa circuit connector 29. The other extremity of the feed- 110 formed bythe flexible wire 16 lead from the de- 115 vice as follows: the lowerextremity, as before noted, is connected to the metallic spool 14.Current from the cylinder 14 is conducted by means vofa brush 30 whichis insulated from the rear frame 11 .and contacts with the rear end ofthe 120 spool 14. The other extremity of the wire 16 is connected to ametallic contact bushing 3l which in turn contacts with a bearing brush32. Thus, the brush 30 and the bearing brush 32 form the terminals forthe variable inductance coil. The connector 29 and the bearing brush 32are carried upon insulating blocks 37 and 38 mounted upon. the rear andfront frames 11 and 10, respectively.

The cylinders 13 and 14 are caused to rotate in unison, and in the samedirection, by means of an upper insulating gear 33 and a lower metallicgear 34, both of which mesh with an insulating drive gear 35. The drivegear 35 is fixed to a drive shaft 36 journalled in the front and rearframes 10 and 11. The drive shaft 36 may be rotated in any desiredmanner, such as by means of a tuning knob 39. v On the drawings the knob39 is shown as projecting on the front surface lof a panel 40.

The journals for all of the shafts in the front and rear frames areprovided with insulated bush.-I

ings 23 as illustrated. The insulating gears 33 and 35 also preventstray currents from flowing to the framework and drive mechanism.

It will be noted that as the drive shaft 36 is rotated the flexible wire16 can be caused to either Wind onto the insulating spool 13 or onto themetallic spool 14 so that the active length of the coil or the number ofactive turns on the spool 13 can be minutely adjusted. The turns uponthe metal spool 14 do not cause inductance because they, being of barewire, contact with the metal surface of the spool so as to eliminate anyindependent action of the turns.

In order that the operator may know the number-of turns upon theinsulated spool 13 at al1 times, an indicating disc 41 is provided, theupper portion of which is visible through a sight opening 42, in thepanel 40. The disc 4l is carried on a sheet metal gear 43 which is freeto rotate about the drive shaft 36 but is prevented from loose rotationthereon by means of a clamp .nut 44. The gear 43 is rotated by means ofa single tooth gear 45 which is secured on the extremity of the lowershaft 17. At each revolution of the shaft 17, the gear 43 will be turnedone tooth space or one dial indication. Since the rotation of the shaft45 corresponds to the rotation of the insulating spool 13 the operatorcan minutely determine the number of turns to a fraction thereof uponthis spool.

In order to maintain the proper inductanceto-capacity ratio throughoutall positions of the variable coil, a variable condenser 46 is employed.The condenser 46 is driven from a worm gear 47 which is journalled inbrackets 48 projecting from the rear frame 11. The worm gear 47 isdriven from a worm 49 secured on the rearward extremity of the lowershaft 17.

The condenser 46 can be of any desired, variable design. Its capacity,however, should be adjusted through adjustment of the Worm gear 47 andthe worm 49, so as to be in the proper ratio at a given setting of thecoil. The worm gears are so designed that this ratio will be maintainedduring the various settings of thecoil.

The device may be used in any desired hookup, a typical one being shownin Fig. 5 in which the leads to the condenser 46 'arebridged across theextremities of the variable coil -formed by the flexible wire 16. Inother words the condenser leads are connected to the brush 30v and thebearing brush 32.

By forming the insulating spool 1,3 with a smaller diameter at the gridextremity as illustrated a greater number of coils are provided at thisextremity for a given length of the wire i6. This allows oscillation atvery high frequencies when but a comparatively short length of the wire16 is inactive. It also allows a relatively coarser adjustment of thetuning at this extremity so as to provide a wider separation of the veryhigh' frequency stations.

To further assist in the latter separation it has been found desirableto cut the coil lgroove on the insulated spool 13 with a variable pitch,such as shown in the alternate form of spool illustrated in Fig. 6. Thisprovides a relatively wider separation of the coil turns on the activecoil as the grid or high frequency extremity is approached. The spiralgrooves in the insulated cylinder also serve to prevent the wire fromsliding down the incline of the tapered surface of the cylinder.

While a specific form of the improvement has been described andillustrated herein, it is desired to be understood that the same may bevaried, within the scope of the appended claims, Without departing fromthe spirit of the invention.

Having thus described the invention, what is claimed and desired securedby Letters Patent 1s:-

1. A spool construction for a variable induction device comprising: ashaft; a hollow, cupshaped spool filled concentrically about said shaftand provided with an open end; a plug fitted over said shaft and closingsaid open end; and a second spool fitted about said shaft and enclosedby said hollow spool and said plug, said plug being fixed to said hollowspool so as to cause the latter to rotate therewith; means for rotatingsaid plug; and means for preventing rotation of said inner spool as saidhollow spool rotates.

2. A spool construction for a variable inductance device comprising: ashaft; a hollow, cupshaped spool filled concentrically about said shaftand provided with an open end; a plug fitted over said shaft and closingsaid open end; and a second spool fitted about said shaft and enclosedby said hollowspool and said plug, means for rotating said hollow spool;means for preventing said shaft from rotating therewith, said innerspool being secured to said shaft; a metallic sleeve surrounding saidshaft but electrically insulated therefrom; and a coil surrounding saidinner spool, the terminals of said coil being connected to said shaftand to said metallic sleeve.

3. A variable inductance device comprising: two

central shaft; a rotatable spool secured to said jj.

rotatable shaft; a first gear secured to said hollow spool; a secondgear secured to said rotatable shaft; a central gear secured to saidcentral shaft and arranged to mesh with saidiir'st and second gears; afixed coil on said fixed spool; and a nexible wire arranged to coil fromsaid hollow spoolto said rotatable spool.

